Add OTLP exporter for OpenTelemetry (#47987)

* Add OTLP exporter for OpenTelemtry

* Fix lint

* Refactore parse settings

* Add configuration for propagation + fix tests

* Fix tests and lint

* Fix alerting tests

* Add coments to config

* Add propagation to custom.ini

pkg/tests/api/alerting/api_notification_channel_test.go

@@ -62,7 +62,10 @@ func TestTestReceivers(t *testing.T) {
 
 		b, err := ioutil.ReadAll(resp.Body)
 		require.NoError(t, err)
-		require.JSONEq(t, `{"traceID":"00000000000000000000000000000000"}`, string(b))
+		res := Response{}
+		err = json.Unmarshal(b, &res)
+		require.NoError(t, err)
+		require.NotEmpty(t, res.TraceID)
 	})
 
 	t.Run("assert working receiver returns OK", func(t *testing.T) {